Joan Bybee and her colleagues present a new theory of the evolution of grammar that links structure and meaning in a way that directly challenges most contemporary versions of generative grammar. This study focuses on the use and meaning of grammatical markers of tense, aspect, and modality and identifies a universal set of grammatical categories. The authors demonstrate that the semantic content of these categories evolves gradually and that this process of evolution is strikingly similar across unrelated languages.

Through a survey of seventy-six languages in twenty-five different phyla, the authors show that the same paths of change occur universally and that movement along these paths is in one direction only. This analysis reveals that lexical substance evolves into grammatical substance through various mechanisms of change, such as metaphorical extension and the conventionalization of implicature. Grammaticization is always accompanied by an increase in frequency of the grammatical marker, providing clear evidence that language use is a major factor in the evolution of synchronic language states.

The Evolution of Grammar has important implications for the development of language and for the study of cognitive processes in general.

Grammaticalization, the process of converting regular lexical items and structures into conventionally interpreted grammatical morphemes, has traditionally been perceived as a syntactic or morphological process. Presenting a wealth of evidence from African languages, the authors argue that the development of grammatical categories is in fact strongly influenced by pragmatic and cognitive forces, factors that are located outside the confines of language structure. They discuss previous models and relate grammaticalization studies to alternative approaches such as localism and natural grammar theory.

This volume challenges theories which describe language as a static system, as well as those which assume that linguistic categorization is based on discrete morpheme types, word classes, or sentence constituents. In contrast, the book's central argument is that both language structure and language use are dynamic phenomena and that linguistic behavior is essentially a creative activity. That creativity manifests itself, for example, in conceptual transfer leading to the encoding of more abstract concepts and of grammatical categories. Another key element of this theory is captured in the term "grammaticalization chain," which refers to a specific kind of linguistic category which cuts across morpheme types and word classes and has both a synchronic and diachronic dimension.